The changelog from the Play store offers a little more detail about the functionality as does their blog post:

Self-destructing photos and the improved photo editor are in the same screen, with easy to use controls presented right there on-screen. You can simply select a photo and start editing easily. The self-destructing photos are only in private chats, but are just as simple to ad in tap the timer and select how long you want it to last for.

The improvements in this version of Telegram don’t stop there with large group chats (100K+ members) getting encrypted Content Distribution Network (CDN) to cache publicly available photos and videos.

The bio may also help in these large chats, letting you peruse who is who, and what they are easily by tapping on an avatar.

Finally, for those who like stickers, you get a heap more room to look through all those sticker packs you’ve accumulated over the last few years.

The update to Telegram (V4.2) is rolling out now, check your Google Play updates section to see if you’ve gotten it yet.